34 MALLET: COAL-FIELDS OF THE nXgA HILLS. 



often contain nodules of clay -ironstone, which are also found in the 

 shales : the most common sizes are from that of a walnut to 8 or 10 

 inches diameter. Layers, also, of the same ore are occasionally inter- 

 banded. Large nodules, and beds a few inches in thickness, of impure 

 limestone are sometimes met with amongst the sandstones and shales. 

 There appears to be a passage from pure clay-ironstone, through 

 calcareous varieties of the same mineral, into more or less ferruginous 

 limestone. Nodules of limestone also occur at times in the coal itself.* 



The grey and brownish -grey shales are very argillaceous, and, 

 where circumstances favor their alteration, decompose into a very tena- 

 cious blue clay. The latter variety of shale passes by degrees into car- 

 bonaceous shale, and it in its turn into coal. Pyrites is present in some of 

 the shale beds as well as in the coal, either scattered through them in 

 nodules, or more minutely disseminated. 



The second section illustrates the frequency of coal seams in some 



parts of the measures, there being no less than 

 Coal seams. 



eight m 130 feet, but none of them over a yard 



thick. Beds, however, greatly thicker than these are not wanting, 



20, 40 and even more than 70 feet of actual coal having been measured 



in one seam. The bed, for instance, south-east of Leap (Makum 



field) contains, 37 feet of coal at least (p. 39). The greatest yet 



found, however, is that in the Namdang nadi, south of Rangring, 



which is over 100 feet thick, and includes at least 75 feet of solid coal 



(p. 42). 



With regard to the lateral extension of the seams, there is evidence 

 that many of them are persistent for considerable distances. In the 

 Makum field, coal is visible in large quantity in every watercourse 

 along the base of the hills between north and north-west of Watto, or 

 for more than a mile. It appears to be on the same horizon throughout, 

 and to belong to one great seam, which, within the above limits, shows 



* For analyses of clay -ironstones and limestones, vide pp. 91, 94. 

 ( 392 ) 



